Recent results on the physical origin of the degradation of GaN-based LEDs and lasers

Abstract

With this paper we describe recent results on the physical mechanisms responsible for the gradual degradation of GaN-based laser diodes and Light-Emitting Diodes (LEDs). The results described in the following were obtained by means of an extensive electrical and optical characterization of laser diodes and LEDs submitted to accelerated stress conditions. The experimental evidence described within this paper demonstrate that: <i>(i)</i> during stress, the threshold current of laser diodes can significantly increase, possibly due to a diffusion-related process; <i>(ii)</i> slope efficiency of laser diodes does not significantly change as a consequence of stress; <i>(iii)</i> LED samples - with the same epitaxial structure of laser diodes - show a significant decrease in optical power during stress time; degradation is more prominent at low measuring current levels, suggesting that it is due to the increase in non-radiative recombination; <i>(iv)</i> the worsening of the optical characteristics of LEDs and laser diodes is significantly correlated to the increase in the defect-related current components. Results described within this paper strongly support the hypothesis that the degradation of laser diodes and LEDs submitted to stress at high current densities (&gt;4 kA/cm²) is due to the increase in the concentration of defects within the active layer of the devices, activated by the high flux of accelerated carriers through the quantum-well region.